Shared Request Grouping in a Computing System

ABSTRACT

A queuing module is configured to determine the presence of at least one shared request in a request queue, and in the event at least one shared request is determined to be present in the queue; determine the presence of a waiting exclusive request located in the queue after the at least one shared request, and in the event a waiting exclusive request is determined to be located in the queue after the at least one shared request: determine whether grouping a new shared request with the at least one shared request violates a deferral limit of the waiting exclusive request; and, in the event grouping the new shared request with the at least one shared request does not violate the deferral limit of the waiting exclusive request, group the new shared request with the at least one shared request.

FIELD

This disclosure relates generally to the field of queuing of requestsfor serialization of resources in a computing system, and morespecifically to grouping of shared requests in a queue of serializationrequests.

DESCRIPTION OF RELATED ART

In a computing system, processes issue various requests for use ofcomputing resources (such as processor time, memory space, or access todata) in the course of execution. Contending processes need to managetheir use of a resource to prevent corruption of the resource. Usually,this is via some serial means of managing concurrent exclusive andshared requesters. Some resource management techniques include pollingfor resource availability, or queuing of requests for use of theresource. Without knowing how the resource is used, the serializationsystem may process the received requests in a first come, first served(FIFO) order. FIFO ordering ensures that if multiple consecutiveresource requests are requested in the proper order (as defined by thedesign of the resource) that deadlock does not occur (i.e., a firstrequest waiting for a first resource that cannot be granted due to asecond request holding the first resource, while the second requestwaits for a second resource that is held by the first request), and thatstarvation (i.e., one request waiting indefinitely for a use of aresource that is repeatedly granted to other requests) of requests alsodoes not occur.

In a z/OS global resource serialization (GRS) system, a request may haveone of two scopes of resource ownership: exclusive or shared. Control ofcomputing resources may be granted to one and only one exclusive requestduring execution of the exclusive request. Shared requests, on the otherhand, may run in parallel with each other; control of the computingresources may be shared by multiple shared requests at a time. Anexclusive request may be followed by an operation that changes thesystem environment or a system resource, such as a write operation; ashared request may include a request that does not change any systemresource, but needs to ensure that the system environment does notchange while it is processing, such as a read operation.

SUMMARY

In one aspect, a method for shared request grouping in a computingsystem includes receiving a new shared request for placement in arequest queue by a queuing module; determining the presence of at leastone shared request in the request queue by the queuing module, and inthe event at least one shared request is determined to be present in thequeue: determining the presence of a waiting exclusive request locatedin the queue after the at least one shared request by the queuingmodule, and in the event a waiting exclusive request is determined to belocated in the queue after the at least one shared request: determiningwhether grouping the new shared request with the at least one sharedrequest violates a deferral limit of the waiting exclusive request bythe queuing module; and in the event grouping the new shared requestwith the at least one shared request does not violate the deferral limitof the waiting exclusive request, grouping the new shared request withthe at least one shared request by the queuing module.

In another aspect, a computer program product comprising a computerreadable storage medium containing computer code that, when executed bya computer, implements a method for shared request grouping, wherein themethod includes receiving a new shared request for placement in arequest queue; determining the presence of at least one shared requestin the request queue, and in the event at least one shared request isdetermined to be present in the queue: determining the presence of awaiting exclusive request located in the queue after the at least oneshared request, and in the event a waiting exclusive request isdetermined to be located in the queue after the at least one sharedrequest: determining whether grouping the new shared request with the atleast one shared request violates a deferral limit of the waitingexclusive request; and, in the event grouping the new shared requestwith the at least one shared request does not violate the deferral limitof the waiting exclusive request, grouping the new shared request withthe at least one shared request.

In another aspect, a queuing module for a computing system is configuredto: receive a new shared request for placement in a request queue;determine the presence of at least one shared request in the requestqueue, and in the event at least one shared request is determined to bepresent in the queue; determine the presence of a waiting exclusiverequest located in the queue after the at least one shared request, andin the event a waiting exclusive request is determined to be located inthe queue after the at least one shared request: determine whethergrouping the new shared request with the at least one shared requestviolates a deferral limit of the waiting exclusive request; and, in theevent grouping the new shared request with the at least one sharedrequest does not violate the deferral limit of the waiting exclusiverequest, group the new shared request with the at least one sharedrequest.

Additional features are realized through the techniques of the presentexemplary embodiment. Other embodiments are described in detail hereinand are considered a part of what is claimed. For a better understandingof the features of the exemplary embodiment, refer to the descriptionand to the drawings.

BRIEF DESCRIPTION OF THE SEVERAL VIEWS OF THE DRAWINGS

Referring now to the drawings wherein like elements are numbered alikein the several FIGURES:

FIG. 1 is a flow diagram illustrating an embodiment of a method forshared request grouping in a computing system.

FIG. 2A-C are schematic block diagrams illustrating embodiments of arequest queue.

FIG. 3A-C are schematic block diagrams illustrating further embodimentsof a request queue.

FIG. 4A-D are schematic block diagrams illustrating further embodimentsof a request queue.

FIG. 5 is a schematic diagram illustrating an embodiment of a computingsystem in which a method for shared request grouping may be implemented.

DETAILED DESCRIPTION

Embodiments of methods for shared request grouping for a queuing modulein a computing system are provided, with exemplary embodiments beingdiscussed below in detail. If exclusive and shared requests arrivealternately in a first come, first served queuing system, lowparallelism of shared request execution may result, with many sharedrequests executing alone due to placement in the queue between twoexclusive requests. This may significantly slow process execution andreduce efficiency of use of resources in the computing system. However,expediting of grouping shared requests together may ensure that multipleshared requests are executed in parallel, improving overall requestthroughput. Also, if one or more shared requests are currently executingand a new shared request is added to the one or more shared requestswhile they are executing, overall system performance is improved, as aprocess issuing the new shared request may not have to change contextdue to the expedited execution of the new shared request. To accomplishthis shared request grouping, waiting exclusive requests may be taggedas deferrable, with an associated deferral limit. The queuing module maygroup a newly received shared request with one or more shared requeststhat are located in the request queue in front of a waiting exclusiverequest, so long as the deferral limit of the waiting exclusive requestis not violated by grouping the new shared request with the one or morequeued shared requests. The definition of deferral limits for exclusiverequests avoids starvation of exclusive requests. Appropriatedesignation of deferral limits for exclusive requests may allow groupingof all outstanding shared requests together, making efficient use ofsystem resources.

The deferral limit for an exclusive request may designate a maximumnumber of requests that are permitted to be queued ahead of theexclusive request before execution of the exclusive request in someembodiments. In some embodiments, the deferral limit may designate anumber of requests permitted to be in the queue ahead of the exclusiverequest, regardless of when the requests ahead of the exclusive requestjoined the queue, or the deferral limit may refer to a number oflater-arriving shared requests that are allowed to jump ahead of theexclusive request, in which case a count of later-arriving sharedrequests that are moved ahead of the exclusive request may be kept. Inother embodiments, the deferral limit may designate a maximum totalamount of time the exclusive request may wait in the queue beforeexecution, or a maximum permitted amount of waiting time that isattributable to moving later-arriving shared requests ahead of theexclusive request. The deferral limit for an exclusive request may bedesignated on a per request basis (based on, for example, the processissuing the exclusive request) in some embodiments, or may be a defaultvalue for all exclusive requests in the queuing system in otherembodiments.

FIG. 1 illustrates an embodiment of a method 100 for shared requestgrouping. The method 100 may be implemented in a queuing module in acomputing system. In block 101, a new shared request is received by thequeuing module. In block 102, it is determined if there are one or moreshared requests already in the queue with which the new shared requestmay be grouped. In various embodiments, the one or more shared requestsalready in the queue may be waiting in the queue, or may be currentlyexecuting. It is then determined if there are any waiting exclusiverequests located in the queue after the one or more shared requests; therespective deferral limit for each waiting exclusive request located inthe queue after the one or more queued shared requests is determined.The deferral limit may designate a total maximum number of requests thatare permitted to be ahead of the exclusive request in the queue, or anumber of shared requests that are permitted to jump ahead of theexclusive request in the queue. The deferral limit may alternatelydesignate a maximum amount of time the exclusive request is permitted towait before execution. In various embodiments, the deferral limit for anexclusive request may be a default value for all exclusive requests inthe queuing system, or may be designated for individual exclusiverequests based on, for example, the process that issued the exclusiverequest. Then, in block 103, any deferral limits determined in block 102are used to determine whether grouping the new shared request with theone or more shared requests violates the deferral limit of any of thewaiting exclusive requests. A number of requests in the queue ahead ofeach waiting exclusive request, a count of shared requests that havebeen moved up in the queue, or an amount of time required to execute thenew shared request in parallel with the one or more shared requests, maybe used to make this determination. If it is determined in block 103that grouping the new shared request with the one or more sharedrequests does not violate the deferral limit of any waiting exclusiverequest, the new shared request is grouped in the queue with the one ormore shared requests in block 104, and the new shared request willexecute with the grouped shared requests before the waiting exclusiverequests. If it is determined in block 103 that grouping the sharedrequest with the one or more shared requests violates the deferral limitof a waiting exclusive request, then the new shared request is placed inthe queue after the waiting exclusive request in block 105. This maycomprise placing the new shared request at the end of the queue in someembodiments, or grouping the new shared request with one or more othershared requests that are located in the queue after the waitingexclusive request in other embodiments (i.e., subject to thedetermination of block 103); placement of the new shared request isperformed such that the deferral limit of no exclusive request in thequeue is violated.

Application of method 100 is illustrated below with respect to FIGS.2A-C, 3A-C, and 4A-D. FIG. 2A illustrates an embodiment of a requestqueue 200A. Request queue 200A includes exclusive request 201 at thefront of the queue 200A, shared request(s) 202, and waiting exclusiverequests 203-204. Each of exclusive requests 201, 203, and 204 has anassociated deferral limit. In various embodiments, shared request(s) 202may include one shared request, or a plurality of grouped sharedrequests. Referring again to FIG. 1, when a new shared request 205 isreceived by a queuing module for the request queue 200 (block 101), thequeuing module determines the respective deferral limits for each ofwaiting exclusive requests 203-204 (block 102), as waiting exclusiverequests 203-204 are located after shared request(s) 202 in the requestqueue 200A. It is then determined if grouping the new shared request 205with shared request(s) 202 and executing the grouped shared requests inparallel violates the respective deferral limits of either of waitingexclusive requests 203-204 (block 103). If grouping the new sharedrequest 205 with shared request(s) 202 and executing the grouped sharedrequests in parallel does not violate the respective deferral limits ofeither of waiting exclusive requests 203-204, then the new sharedrequest 205 is grouped with shared request(s) 202 to form grouped sharedrequests 206 (block 104), as shown in updated queue 200B of FIG. 2B. Thegrouped shared requests 206 are executed in parallel when they arrive atthe front of the queue (in this example, after completion of exclusiverequest 201). Otherwise, the new shared request 205 is placed at the endof the queue after exclusive request 204 (block 105), as shown inupdated queue 200C of FIG. 2C. Request queue 200A and updated queues200B-C are shown for illustrative purposes only; a request queue mayinclude any number of exclusive requests, and any number of grouped orungrouped shared requests in various embodiments, subject to the method100 outlined in FIG. 1.

FIG. 3A illustrates another embodiment of a request queue 300A. Requestqueue 300A includes shared request(s) 301 at the front of the queue 300A(i.e., shared request(s) 301 are currently executing), and waitingexclusive requests 302-303. Each of exclusive requests 302-303 has anassociated deferral limit. In various embodiments, shared request(s) 301may include one shared request, or a plurality of grouped sharedrequests. Referring again to FIG. 1, when a new shared request 304 isreceived by a queuing module for the request queue 300A (block 101), thequeuing module determines the respective deferral limits for each ofwaiting exclusive requests 302-303 (block 102), as waiting exclusiverequests 302-303. are located after shared request(s) 301 in the requestqueue 300A. It is then determined if grouping the new shared request 304with shared request(s) 301 and executing the grouped shared requests inparallel violates the respective deferral limits of either of waitingexclusive requests 302-303 (block 103). If grouping the new sharedrequest 304 with shared request(s) 301 and executing the grouped sharedrequests in parallel does not violate the respective deferral limits ofeither of waiting exclusive requests 302-303, then the new sharedrequest 304 is grouped with shared request(s) 301 to form grouped sharedrequests 305 (block 104), as shown in updated queue 300B of FIG. 3B. Thegrouped shared requests 305 are executed in parallel, allowing theprocess issuing the new shared request 304 to not have to change context(i.e., suspend or resume), as the process may continue to execute withthe expedited execution of new shared request 304. Otherwise, the newshared request 304 is placed at the end of the queue after exclusiverequest 303 (block 105), as shown in updated queue 300C of FIG. 3C.Request queue 300A and updated queues 300B-C are shown for illustrativepurposes only; a request queue may include any number of exclusiverequests, and any number of grouped or ungrouped shared requests invarious embodiments, subject to the method 100 outlined in FIG. 1.

FIG. 4A illustrates another embodiment of a request queue 400A. Requestqueue 400A includes exclusive request 401 at the front of the queue400A, shared request(s) 402, waiting exclusive request 403, sharedrequest(s) 404, and exclusive request 405. Each of exclusive requests401, 403, and 405 has an associated deferral limit. In variousembodiments, each of shared request(s) 402 and 404 may include oneshared request, or a plurality of grouped shared requests. Referringagain to FIG. 1, when a new shared request 406 is received by a queuingmodule for the request queue 400A (block 101), the queuing moduledetermines the respective deferral limits for each of waiting exclusiverequests 403 and 405 (block 102), as waiting exclusive requests 403 islocated after shared request(s) 402, and waiting exclusive requests 405is located after shared request(s) 402 and 404. It is then determined ifgrouping the new shared request 406 with shared request(s) 402 or withshared request(s) 404 violates the respective deferral limits of eitherof waiting exclusive requests 403 or 405 (block 103). If grouping thenew shared request 406 with shared request(s) 402 and executing thegrouped shared requests in parallel does not violate the respectivedeferral limits of either of waiting exclusive requests 403 or 405, thenthe new shared request 406 is grouped with shared request(s) 402 to formgrouped shared requests 407 (block 104), as shown in updated queue 400Bof FIG. 4B. The grouped shared requests 407 are executed in parallelwhen they arrive at the front of the queue (in this example, aftercompletion of exclusive request 401, and before exclusive requests 403and 405). If grouping new shared request 406 with shared request(s) 402violates the deferral limit of exclusive request 403, but does notviolate the deferral limit of exclusive request 405, the new sharedrequest 406 is grouped with shared request(s) 404 ahead of exclusiverequest 405 but behind exclusive request 403, forming grouped sharedrequests 408, as shown in updated queue 400C of FIG. 4C. If grouping thenew shared request 406 with either of shared request(s) 402 or 404violates the deferral limit of exclusive request 405, the new sharedrequest 406 is placed at the end of the queue after exclusive request405 (block 105), as shown in updated queue 400D of FIG. 4D. Asillustrated by FIGS. 4A-D, a new shared request will be grouped in thequeue with the first shared request(s) in the queue that may be groupedwith the new shared request without violating the deferral limit of anywaiting exclusive request, or the new shared request will be placed atthe end of the queue. Request queue 400A and updated queues 400B-D areshown for illustrative purposes only; a request queue may include anynumber of exclusive requests, and any number of grouped or ungroupedshared requests in various embodiments, subject to the method 100outlined in FIG. 1.

FIG. 5 illustrates an example of a computer 500 which may be utilized byexemplary embodiments of a method for shared request grouping andexclusive request deferral as embodied in software. Various operationsdiscussed above may utilize the capabilities of the computer 500. One ormore of the capabilities of the computer 500 may be incorporated in anyelement, module, application, and/or component discussed herein. Forexample, a queuing module that implements method 100 of FIG. 1 may beimplemented in operating system 550, and exclusive and shared requestshandled by the queuing module may be executed by processor 570.

The computer 500 includes, but is not limited to, personal computers(PCs), workstations, laptops, PDAs, palm devices, servers, storages, andthe like. Generally, in terms of hardware architecture, the computer 500may include one or more processors 510, memory 520, and one or moreinput and/or output (I/O) devices 570 that are communicatively coupledvia a local interface (not shown). The local interface can be, forexample but not limited to, one or more buses or other wired or wirelessconnections, as is known in the art. The local interface may haveadditional elements, such as controllers, buffers (caches), drivers,repeaters, and receivers, to enable communications. Further, the localinterface may include address, control, and/or data connections toenable appropriate communications among the aforementioned components.

The processor 510 is a hardware device for executing software that canbe stored in the memory 520. The processor 510 can be virtually anycustom made or commercially available processor, a central processingunit (CPU), a digital signal processor (DSP), or an auxiliary processoramong several processors associated with the computer 500, and theprocessor 510 may be a semiconductor based microprocessor (in the formof a microchip) or a macroprocessor.

The memory 520 can include any one or combination of volatile memoryelements (e.g., random access memory (RAM), such as dynamic randomaccess memory (DRAM), static random access memory (SRAM), etc.) andnonvolatile memory elements (e.g., ROM, erasable programmable read onlymemory (EPROM), electronically erasable programmable read only memory(EEPROM), programmable read only memory (PROM), tape, compact disc readonly memory (CD-ROM), disk, diskette, cartridge, cassette or the like,etc.). Moreover, the memory 520 may incorporate electronic, magnetic,optical, and/or other types of storage media. Note that the memory 520can have a distributed architecture, where various components aresituated remote from one another, but can be accessed by the processor510.

The software in the memory 520 may include one or more separateprograms, each of which comprises an ordered listing of executableinstructions for implementing logical functions. The software in thememory 520 includes a suitable operating system (O/S) 550, compiler 540,source code 530, and one or more applications 560 in accordance withexemplary embodiments. As illustrated, the application 560 comprisesnumerous functional components for implementing the features andoperations of the exemplary embodiments. The application 560 of thecomputer 500 may represent various applications, computational units,logic, functional units, processes, operations, virtual entities, and/ormodules in accordance with exemplary embodiments, but the application560 is not meant to be a limitation.

The operating system 550 controls the execution of other computerprograms, and provides scheduling, input-output control, file and datamanagement, memory management, and communication control and relatedservices. It is contemplated by the inventors that the application 560for implementing exemplary embodiments may be applicable on allcommercially available operating systems.

Application 560 may be a source program, executable program (objectcode), script, or any other entity comprising a set of instructions tobe performed. When a source program, then the program is usuallytranslated via a compiler (such as the compiler 540), assembler,interpreter, or the like, which may or may not be included within thememory 520, so as to operate properly in connection with the O/S 550.Furthermore, the application 560 can be written as an object orientedprogramming language, which has classes of data and methods, or aprocedure programming language, which has routines, subroutines, and/orfunctions, for example but not limited to, C, C++, C#, Pascal, BASIC,API calls, HTML, XHTML, XML, ASP scripts, FORTRAN, COBOL, Perl, Java,ADA, .NET, and the like.

The I/O devices 570 may include input devices such as, for example butnot limited to, a mouse, keyboard, scanner, microphone, camera, etc.Furthermore, the I/O devices 570 may also include output devices, forexample but not limited to a printer, display, etc. Finally, the I/Odevices 570 may further include devices that communicate both inputs andoutputs, for instance but not limited to, a NIC or modulator/demodulator(for accessing remote devices, other files, devices, systems, or anetwork), a radio frequency (RF) or other transceiver, a telephonicinterface, a bridge, a router, etc. The I/O devices 570 also includecomponents for communicating over various networks, such as the Internetor intranet.

If the computer 500 is a PC, workstation, intelligent device or thelike, the software in the memory 520 may further include a basic inputoutput system (BIOS) (omitted for simplicity). The BIOS is a set ofessential software routines that initialize and test hardware atstartup, start the O/S 550, and support the transfer of data among thehardware devices. The BIOS is stored in some type of read-only-memory,such as ROM, PROM, EPROM, EEPROM or the like, so that the BIOS can beexecuted when the computer 500 is activated.

When the computer 500 is in operation, the processor 510 is configuredto execute software stored within the memory 520, to communicate data toand from the memory 520, and to generally control operations of thecomputer 500 pursuant to the software. The application 560 and the O/S550 are read, in whole or in part, by the processor 510, perhapsbuffered within the processor 510, and then executed.

When the application 560 is implemented in software it should be notedthat the application 560 can be stored on virtually any computerreadable medium for use by or in connection with any computer relatedsystem or method. In the context of this document, a computer readablemedium may be an electronic, magnetic, optical, or other physical deviceor means that can contain or store a computer program for use by or inconnection with a computer related system or method.

The application 560 can be embodied in any computer-readable medium foruse by or in connection with an instruction execution system, apparatus,or device, such as a computer-based system, processor-containing system,or other system that can fetch the instructions from the instructionexecution system, apparatus, or device and execute the instructions. Inthe context of this document, a “computer-readable medium” can be anymeans that can store, communicate, propagate, or transport the programfor use by or in connection with the instruction execution system,apparatus, or device. The computer readable medium can be, for examplebut not limited to, an electronic, magnetic, optical, electromagnetic,infrared, or semiconductor system, apparatus, device, or propagationmedium.

More specific examples (a nonexhaustive list) of the computer-readablemedium may include the following: an electrical connection (electronic)having one or more wires, a portable computer diskette (magnetic oroptical), a random access memory (RAM) (electronic), a read-only memory(ROM) (electronic), an erasable programmable read-only memory (EPROM,EEPROM, or Flash memory) (electronic), an optical fiber (optical), and aportable compact disc memory (CDROM, CD R/W) (optical). Note that thecomputer-readable medium could even be paper or another suitable medium,upon which the program is printed or punched, as the program can beelectronically captured, via for instance optical scanning of the paperor other medium, then compiled, interpreted or otherwise processed in asuitable manner if necessary, and then stored in a computer memory.

In exemplary embodiments, where the application 560 is implemented inhardware, the application 560 can be implemented with any one or acombination of the following technologies, which are well known in theart: a discrete logic circuit(s) having logic gates for implementinglogic functions upon data signals, an application specific integratedcircuit (ASIC) having appropriate combinational logic gates, aprogrammable gate array(s) (PGA), a field programmable gate array(FPGA), etc.

The technical effects and benefits of exemplary embodiments includeimprovement of parallelization and throughput in a computing system.

The terminology used herein is for the purpose of describing particularembodiments only and is not intended to be limiting of the invention. Asused herein, the singular forms “a”, “an”, and “the” are intended toinclude the plural forms as well, unless the context clearly indicatesotherwise. It will be further understood that the terms “comprises”and/or “comprising,” when used in this specification, specify thepresence of stated features, integers, steps, operations, elements,and/or components, but do not preclude the presence or addition of oneor more other features, integers, steps, operations, elements,components, and/or groups thereof.

The corresponding structures, materials, acts, and equivalents of allmeans or step plus function elements in the claims below are intended toinclude any structure, material, or act for performing the function incombination with other claimed elements as specifically claimed. Thedescription of the present invention has been presented for purposes ofillustration and description, but is not intended to be exhaustive orlimited to the invention in the form disclosed. Many modifications andvariations will be apparent to those of ordinary skill in the artwithout departing from the scope and spirit of the invention. Theembodiment was chosen and described in order to best explain theprinciples of the invention and the practical application, and to enableothers of ordinary skill in the art to understand the invention forvarious embodiments with various modifications as are suited to theparticular use contemplated.

1. A method for shared request grouping in a computing system, themethod comprising: receiving a new shared request for placement in arequest queue by a queuing module; determining the presence of at leastone shared request in the request queue by the queuing module, and inthe event at least one shared request is determined to be present in thequeue: determining the presence of a waiting exclusive request locatedin the queue after the at least one shared request by the queuingmodule, and in the event a waiting exclusive request is determined to belocated in the queue after the at least one shared request: determiningwhether grouping the new shared request with the at least one sharedrequest violates a deferral limit of the waiting exclusive request bythe queuing module; and in the event grouping the new shared requestwith the at least one shared request does not violate the deferral limitof the waiting exclusive request, grouping the new shared request withthe at least one shared request by the queuing module.
 2. The method ofclaim 1, further comprising executing the new shared request and the atleast one shared request in parallel before executing the waitingexclusive request by the computing system.
 3. The method of claim 1,further comprising: in the event grouping the new shared request withthe at least one shared request violates the deferral limit of thewaiting exclusive request, placing the new shared request in the queueafter the waiting exclusive request by the queuing module.
 4. The methodof claim 1, wherein the deferral limit of a waiting exclusive requestcomprises a maximum number of requests that are permitted to executebefore the waiting exclusive request, and wherein determining whethergrouping the new shared request with the at least one shared requestviolates the deferral limit of the waiting exclusive request by thequeuing module comprises: determining the deferral limit of the waitingexclusive request by the queuing module; determining a number ofrequests in the queue ahead of the waiting exclusive request by thequeuing module; in the event that the number of requests in the queueahead of the waiting exclusive request is less than or equal to thedeferral limit of the waiting exclusive request if the new sharedrequest is grouped with the at least one shared request, determiningthat grouping the new shared request with the at least one sharedrequest does not violate the deferral limit by the queuing module; andin the event that the number of requests in the queue ahead of thewaiting exclusive request is greater than the deferral limit of thewaiting exclusive request if the new shared request is grouped with theat least one shared request, determining that grouping the new sharedrequest with the at least one shared request violates the deferral limitby the queuing module.
 5. The method of claim 1, wherein the deferrallimit of a waiting exclusive request comprises a maximum number oflater-arriving shared requests that are permitted to be grouped in frontof the waiting exclusive request, and wherein determining whethergrouping the new shared request with the at least one shared requestviolates the deferral limit of the waiting exclusive request by thequeuing module comprises: determining the deferral limit of the waitingexclusive request by the queuing module; determining a number oflater-arriving shared requests in the queue that have been grouped infront of the waiting exclusive request by the queuing module; in theevent that the number of later-arriving shared requests in the queuethat have been grouped in front of the waiting exclusive request is lessthan the deferral limit of the waiting exclusive request if the newshared request is grouped with the at least one shared request,determining that grouping the new shared request with the at least oneshared request does not violate the deferral limit by the queuingmodule; and in the event that the number of later-arriving sharedrequests in the queue that have been grouped in front of the waitingexclusive request is greater than the deferral limit of the waitingexclusive request if the new shared request is grouped with the at leastone shared request, determining that grouping the new shared requestwith the at least one shared request violates the deferral limit by thequeuing module.
 6. The method of claim 1, wherein the deferral limit ofa waiting exclusive request comprises a maximum amount of time that thewaiting exclusive request is permitted to wait before execution, andwherein determining whether grouping the new shared request with the atleast one shared request violates the deferral limit of the waitingexclusive request by the queuing module comprises: determining thedeferral limit of the waiting exclusive request by the queuing module;determining whether the waiting exclusive request will be executedbefore expiration of the deferral limit if the new shared request isgrouped with the at least one shared request by the queuing module; inthe event that the waiting exclusive request will be executed beforeexpiration of the deferral limit if the new shared request is groupedwith the at least one shared request, determining that grouping the newshared request with the at least one shared request does not violate thedeferral limit by the queuing module; and in the event that the waitingexclusive request will not be executed before expiration of the deferrallimit if the new shared request is grouped with the at least one sharedrequest, determining that grouping the new shared request with the atleast one queued shared request violates the deferral limit by thequeuing module.
 7. The method of claim 1, wherein the deferral limit ofa waiting exclusive request comprises a maximum permitted amount ofwaiting time for the exclusive request that is attributable tolater-arriving shared requests being grouped ahead of the waitingexclusive request, and wherein determining whether grouping the newshared request with the at least one shared request violates thedeferral limit of the waiting exclusive request by the queuing modulecomprises: determining the deferral limit of the waiting exclusiverequest by the queuing module; determining an amount of waiting time forthe exclusive request that is attributable to later-arriving sharedrequests being grouped ahead of the waiting exclusive request if the newshared request is grouped with the at least one shared request by thequeuing module; in the event that the amount of waiting time for theexclusive request that is attributable to later-arriving shared requestsbeing grouped ahead of the waiting exclusive request if the new sharedrequest is grouped with the at least one shared request is less than thedeferral limit, determining that grouping the new shared request withthe at least one shared request does not violate the deferral limit bythe queuing module; and in the event that the amount of waiting time forthe exclusive request that is attributable to later-arriving sharedrequests being grouped ahead of the waiting exclusive request if the newshared request is grouped with the at least one shared request isgreater than the deferral limit, determining that grouping the newshared request with the at least one queued shared request violates thedeferral limit by the queuing module.
 8. The method of claim 1, whereinthe deferral limit of the waiting exclusive request is designated basedon an issuer of the exclusive request.
 9. The method of claim 1, whereinthe deferral limit of the waiting exclusive request is a default valueset by the queuing module.
 10. A computer program product comprising acomputer readable storage medium containing computer code that, whenexecuted by a computer, implements a method for shared request grouping,wherein the method comprises: receiving a new shared request forplacement in a request queue; determining the presence of at least oneshared request in the request queue, and in the event at least oneshared request is determined to be present in the queue: determining thepresence of a waiting exclusive request located in the queue after theat least one shared request, and in the event a waiting exclusiverequest is determined to be located in the queue after the at least oneshared request: determining whether grouping the new shared request withthe at least one shared request violates a deferral limit of the waitingexclusive request; and in the event grouping the new shared request withthe at least one shared request does not violate the deferral limit ofthe waiting exclusive request, grouping the new shared request with theat least one shared request.
 11. The computer program product accordingto claim 10, further comprising executing the new shared request and theat least one shared request in parallel before executing the waitingexclusive request by the computing system.
 12. The computer programproduct according to claim 10, further comprising: in the event groupingthe new shared request with the at least one shared request violates thedeferral limit of the waiting exclusive request, placing the new sharedrequest in the queue after the waiting exclusive request.
 13. Thecomputer program product according to claim 10, wherein the deferrallimit of a waiting exclusive request comprises a maximum number ofrequests that are permitted to execute before the waiting exclusiverequest, and wherein determining whether grouping the new shared requestwith the at least one shared request violates the deferral limit of thewaiting exclusive request comprises: determining the deferral limit ofthe waiting exclusive request; determining a number of requests in thequeue ahead of the waiting exclusive request; in the event that thenumber of requests in the queue ahead of the waiting exclusive requestis less than the deferral limit of the waiting exclusive request if thenew shared request is grouped with the at least one shared request,determining that grouping the new shared request with the at least oneshared request does not violate the deferral limit; and in the eventthat the number of requests in the queue ahead of the waiting exclusiverequest is greater than the deferral limit of the waiting exclusiverequest if the new shared request is grouped with the at least oneshared request, determining that grouping the new shared request withthe at least one shared request violates the deferral limit.
 14. Thecomputer program product according to claim 10, wherein the deferrallimit of a waiting exclusive request comprises a maximum amount of timethat the waiting exclusive request is permitted to wait beforeexecution, and wherein determining whether grouping the new sharedrequest with the at least one shared request violates the deferral limitof the waiting exclusive request comprises: determining the deferrallimit of the waiting exclusive request; determining whether the waitingexclusive request will be executed before expiration of the deferrallimit if the new shared request is grouped with the at least one sharedrequest; in the event that the waiting exclusive request will beexecuted before expiration of the deferral limit if the new sharedrequest is grouped with the at least one shared request, determiningthat grouping the new shared request with the at least one sharedrequest does not violate the deferral limit; and in the event that thewaiting exclusive request will not be executed before expiration of thedeferral limit if the new shared request is grouped with the at leastone shared request, determining that grouping the new shared requestwith the at least one shared request violates the deferral limit. 15.The computer program product according to claim 10, wherein the deferrallimit of the waiting exclusive request is designated based on an issuerof the exclusive request.
 16. The computer program product according toclaim 10, wherein the deferral limit of the waiting exclusive request isa default value.
 17. A queuing module for a computing system, thequeuing module configured to: receive a new shared request for placementin a request queue; determine the presence of at least one sharedrequest in the request queue, and in the event at least one sharedrequest is determined to be present in the queue: determine the presenceof a waiting exclusive request located in the queue after the at leastone shared request, and in the event a waiting exclusive request isdetermined to be located in the queue after the at least one sharedrequest: determine whether grouping the new shared request with the atleast one shared request violates a deferral limit of the waitingexclusive request; and in the event grouping the new shared request withthe at least one shared request does not violate the deferral limit ofthe waiting exclusive request, group the new shared request with the atleast one shared request.
 18. The queuing module of claim 17, furtherconfigured to: in the event grouping the new shared request with the atleast one shared request violates the deferral limit of the waitingexclusive request, placing the new shared request in the queue after thewaiting exclusive request.
 19. The queuing module of claim 17, whereinthe deferral limit of the waiting exclusive request is designated basedon an issuer of the exclusive request.
 20. The queuing module of claim17, wherein the deferral limit of the waiting exclusive request is adefault value by the queuing module.